1. Field of the Invention
The present invention relates to a light projection unit and a light projection device, and more particularly to a light projection unit and a light projection device that include a fluorescent member to which laser light is applied.
2. Description of the Related Art
Conventionally, light projection devices are known that include a fluorescent member to which laser light is applied (for example, see WO 2007/105647).
In WO 2007/105647 (pages 11 and 12 and FIG. 3) mentioned above, a light emission device (light projection device) is disclosed that includes a laser diode (laser generator), a light collection lens which is formed with a biconvex lens for collecting laser light emitted from the laser diode and a fluorescent member to which the laser light from the light collection lens is applied. In this light emission device, the laser light emitted from the laser diode is collected by the light collection lens and is applied to the fluorescent member. Then, the laser light is converted in wavelength by the fluorescent member into fluorescent light, and the fluorescent light is emitted to the outside.
However, the inventor of the present application has fully examined the light emission device of WO 2007/105647, and thereby has found the following problems. Specifically, as shown in FIG. 38, when the laser light is applied to the fluorescent member 1003 through the light collection lens 1002, a portion of the application surface 1003a of the fluorescent member 1003 (for example, a light collection point P1001) appears where the light density of the laser light is excessively increased. When the light density is excessively increased on the application surface 1003a of the fluorescent member 1003, it is likely that a fluorescent body and a binder contained in the fluorescent member 1003 are degraded by heat or are degraded by undergoing a chemical reaction caused by light.
One way to reduce the production of the portion of the application surface 1003a of the fluorescent member 1003 where the light density is excessively increased is to displace, as shown in FIG. 39, the application surface 1003a of the fluorescent member 1003 from the light collection point P1001 (see FIG. 38) of the laser light. However, as shown in FIG. 40, the light intensity distribution of the laser light is not uniform but is formed in the shape of Gaussian distribution. Hence, it has been found that, even when the application surface 1003a is displaced from the light collection point P1001 of the laser light, the portion of the application surface 1003a where the light density is excessively increased may be produced.
When vibration, aged deterioration or the like causes the displacement of the laser diode 1001, the light collection lens 1002 or the fluorescent member 1003, the light density on the application surface 1003a of the fluorescent member 1003 is greatly changed. Hence, it has been found that the portion where the light density is excessively increased is produced depending on the direction of the displacement.